There has long been a need for a medical patch particularly for use as a wound dressing which is thin, soft, pliable and elastic, yet high in water vapor transmission and abrasion resistance and which does not promote the growth of bacteria.
Presently available bandages made of materials such as cotton are undesirable because they retain water, serve as growth media for bacteria, and soak up tissue pieces and blood which clots, causing adhesion to the wound and trauma during removal.
Bandages made of plastic materials to decrease the undesirable water absorption of cotton wound dressings are available. Unfortunately, problems due to lack of oxygen transmission through the plastic result from the use of many plastic materials. Indeed, holes are punched through the plastic covering to allow the transmission of some oxygen to the skin below. Such constructions do not provide a barrier to low surface tension aqueous solutions, e.g. washing-up liquid (which will also allow bacteria to penetrate). Silicone coatings have been applied to the area of the bandage adjacent to the wound to prevent adhesion. These coatings did not significantly decrease the problem of the bandage sticking to the wound, and do nothing to reduce the blocked oxygen problem.
In further attempts to overcome the adhesion and permeability problems, polyurethane and other plastic dressings were tried. For example, U.S. Pat. No. 3,975,567 to Lock discloses a pressure and heat-treated polyurethane foam which is lyophilic and U.S. Pat. No. 3,870,593 to Elton et al. discloses a polymeric film comprised of finely divided particles of non-hygroscopic inorganic salt dispersed in a suitable polymer.
Other polyurethanes which polymerize upon exposure to ultraviolet light were also developed. The majority of these UV-curable polyurethanes were designed for use as orthopedic casts, for example, U.S. Pat. No. 4,209,605 discloses such a cast. None of these compositions managed to combine the properties of softness, oxygen and water vapor permeability, flexibility, and thixotropy.
The desired material for use as a wound dressing or bandage must be permeable to water vapor, but not permeable to liquid water, microorganisms and particles of dirt. The material may also be anisotropic, by which is meant that the fabric stretches more in one direction than in the other. This characteristic allows the dressing to stretch in the direction of the skin to which it is applied and allows for easy application.
The material should also be thin so that the dressing is not easily bumped or displaced by contact with outside sources. Other bandages which use a knitted fabric result in a very voluminous bandage. See, for example, U.S. Pat. No. 4,236,550 to Braun et al. and U.S. Pat. No. 4,391,106 to Schafer et al. Thinner wound dressings presently available and formed of polyurethane often require two or more trained medical personnel for proper application because of their thinness, elasticity and tendency to stick to themselves during application.